A flowing Ketelbey piece (4)

I believe the answer is:

elbe

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'a flowing' is the definition.
Both the definition and answer are singular nouns.
Perhaps there's a link between them I don't understand?

'ketelbey piece' is the wordplay.
'piece' says the answer is hidden in the clue.
'ELBE' is hidden within 'ketelbey'.

Can you help me to learn more?

(Other definitions for elbe that I've seen before include "Dresden and Hamburg's river" , "A major German river" , "River flowing through Dresden and Hamburg" , "Flower" , "River rising in the Czech Republic and flowing into the North Sea" .)

I've seen this clue in the Evening Standard.

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